Patent Publication Number: US-6901629-B2

Title: Heavy duty molded equipment slide

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a molded slide having a slidability and load bearing capability making it suitable for use in moving furniture or other heavy objects across a floor. 
   2. Brief Description of the Prior Art 
   It is often necessary to move office furniture, such as desks, bookcases, partitions and filing cabinets, about an office. The need to move the furniture may arise from a desire to reconfigure the office space or to perform maintenance, such as carpet cleaning or carpet removal and replacement. For example, modular carpet is designed to be installed in occupied office areas with furniture and equipment in place. During installation, furniture and equipment are moved a short distance or lifted while the old flooring is removed and squares of new modular carpet installed. The office furniture or equipment is then slid or lowered into place, permitting installation of new carpet without breaking down work stations, disrupting telecommunication or computer hookups and avoiding business interruptions. 
   With the exception of moving furniture up and down stairways, it has been found that placing a slide under the object and sliding the furniture or equipment is preferred over using a hand truck or some other device for lifting the furniture. In U.S. Pat. No. 5,469,599 to Wurdack, ultra high molecular weight polyethylene was identified as being suitable for use as a slide for moving furniture when provided as a flat plate having a thickness between about 0.05 inches and 0.15 inches and having a diameter from about 4 inches to 10 inches. The disks were cut from sheets of ultra high molecular weight polyethylene which are formed industrially by skiving large blocks of the plastic. A non-slip pad of synthetic plastic material was then glued to the top surface of the disk. 
   In U.S. Pat. No. 5,802,669 to Wurdack, polyoxymethylene, an acetal homopolymer, was identified as being suitable for use as a slide for moving furniture when provided as a molded plate with an upturned edge forming a recess into which a non-slip pad could be glued. This was an improvement over the &#39;599 patent, inter alia, in that ultra high molecular weight polyethylene cannot be molded and machining a recess into the top surface was cost prohibitive. The plate in the &#39;669 patent had a thickness between about 0.05 inches and 0.15 inches and had a diameter between about 4 and 10 inches. The homopolymer had a coefficient of friction of about 0.3 and a pressure versus velocity of about 750 or better. The coefficient of friction is a measure of how well the plate slid and the pressure versus velocity number is an indication of how well the plate stood up under loading conditions. The slidability and load bearing capabilities of the &#39;669 slide were better than the &#39;599 slide. However, the recess in the plate was shallow and the non-slip pad was made out of foamed ethylvinylacetate or latex rubber and was stiff. In use, the legs or base of the object being moved tended to slip off the slide and break the rim off the plate. 
   The load bearing demands on a slide can be extreme as some office furniture and equipment is very heavy (e.g., lateral files weighing over 2,000 pounds) calling for a slide with better load bearing capability. Slidability demands can also be extreme for example when the furniture and other equipment must be slid over a concrete floor. Hence, there remains room for improvement to meet the full range of moving conditions in addition to tackling the slipping-off the slide problem. 
   BRIEF SUMMARY OF THE INVENTION 
   In view of the above, it is an object of the present invention to provide a slide having slidability and load bearing capability for use in moving heavy office furniture and equipment. It is another object to provide a slide configured such that the floor contacting portion of an object placed on the slide does not tend to come off the slide. Other objects and features of the invention will be in part apparent and in part pointed out hereinafter. 
   In accordance with the invention, a slide for use in moving heavy pieces of furniture or other heavy objects across a floor has an upwardly cupped plate formed of an acetal copolymer matrix into which a lubricant is incorporated and has a coefficient of friction of less than 0.2. A non-slip pad formed of synthetic plastic material is seated in a recess provided in an upper face of the plate. The slide has an upstanding rim about a periphery of the recess and a lower face of the plate rises above the floor when the slide is partially inserted beneath a floor contacting portion of the furniture or object. 
   The invention summarized above comprises the constructions hereinafter described, the scope of the invention being indicated by the subjoined claims. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     In the accompanying drawings, in which one of various possible embodiments of the invention is illustrated, corresponding reference characters refer to corresponding parts throughout the several views of the drawings in which: 
       FIG. 1  is a cross-section taken along the plane of  1 — 1  in  FIG. 2  of a slide for moving heavy objects in accordance with the present invention; 
       FIG. 2  is a plan view of the slide; and, 
       FIG. 3  is a cross-section similar to  FIG. 1  but showing the slide partially inserted under a floor contacting portion of the heavy object to be moved. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the drawings more particularly by reference character, reference numeral  10  refers to a slide for moving furniture and other heavy objects across a floor  11 . Slide  10  is molded from an acetal copolymer matrix into which a lubricant is incorporated. The slide has a coefficient of friction of less than 0.2. As shown in  FIGS. 1–2 , slide  10  has an upper and lower face  12 ,  14 , respectively and is molded as an upwardly cupped plate  16  with a recess  18  in upper face  12  for receipt of a non-slip resilient pad  20 . An upstanding rim  22  is formed around recess  18  and plate  16  is sufficiently cupped that it can be spun on a surface. Plate  16  has adequate compressive strength that it does not flatten along its forward edge  24  when partially inserted beneath a floor contacting portion  26  of a heavy object  28  as shown in  FIG. 3 . 
   Slide  10  is about 3 to 10 inches in diameter, preferably about 5 to 8 inches and most preferably about 6 inches. Plate  16  has a thickness between about 0.05 and 0.15 inches, preferably about 0.08 and 0.12 inches and most preferably about 0.09 inches. Rim  22  is about 0.10 to 0.35 inches high, preferably about 0.12 to 0.30 inches and most preferably about 0.25 inches. Recess  18  is about 0.06 to 0.25 inches deep, preferably about 0.08 to 0.20 inches and most preferably about 0.15 inches. Lower face  14  of plate  16  is elevated above floor  11  between about 0.05 and 0.15 inches, preferably between about 0.8 and 0.12 inches and most preferably about 0.10 inches. As shown in  FIG. 2 , slide  10  has an outside diameter of 6.00 inches and recess  18  has an outside diameter of 5.60 inches. Slide  10  as compared to the slide described in the &#39;699 patent is stronger and heavier (e.g., a five-inch slide from the &#39;699 patent formed of oxymethylene homopolymer weighs 38 grams whereas a six-inch slide formed of a lubricated oxymethylene copolymer in accordance with the present invention weighs 70 grams). 
   When rim  22  of slide  10  is pressed down as shown in  FIG. 3  under the weight of a heavy load, lower face  14  at forward edge  24  of plate  16  is off floor  11  between about 0.50 and 1.50 inches, preferably about 0.75 and 1.25 inches and most preferably about 1.00 inch. This makes it easier for slide  10  to cam over a carpet  30  as shown in  FIG. 3  or some other obstruction such as a threshold. For comparison, a slide as described in the &#39;699 patent tends to flatten under a heavy load and instead of rising above the floor along its forward edge, it may conform to the floor such that the forward edge stubs into the carpet or floor irregularities, making it more difficult to slide the object. The forward edge of the slides in the &#39;699 patent sometimes chips, making sliding of the damaged slide even more difficult and the slide unsuitable to be used again. 
   Acetal copolymers are well known in the art. Such copolymers are characterized as having recurring oxymethylene groups, i.e., —CH 2 O—, interspersed with oxy(higher)alkylene groups, e.g., —CH 2 CH 2 O—. Acetal copolymers have better impact strength and coefficient of friction than oxymethylene homopolymers from which the slides in the &#39;699 patent were formed. The addition of a lubricant to the acetal copolymer matrix further improves the impact strength and coefficient of friction of slide  10 . 
   Acetal copolymers can be internally lubricated with polytetrafluoroethylene (PTFE) resins. PTFE may be added to a larger quantity of molten acetal copolymer. Slide  10  molded from such a mixture has better wear resistance and there is a reduction in friction. The mechanism for these improvements may be the formation of a dry film of PTFE between slide  10  and floor surface  11 . This film may be formed during the break-in period for the slide, as randomly dispersed particles of PTFE are sheared to form a film on the bearing surface of lower face  14 . From 1 to 30 weight percent of PTFE may be added to the acetal copolymer. Lesser amounts (e.g., about 2 weight percent) may be preferred because of cost and other considerations. 
   An oxymethylene copolymer lubricated with PTFE is commercially available from Ticona, a business of Celanese AG, under the designation CELCON LW90F2. This resin is a CELCON M90 based acetal copolymer formulated with 2 weight percent PTFE. It has excellent wear properties and a static coefficient of friction against steel of 0.12 as measured by ASTM D1894. This compares very favorably against DELRIN 500 which is an oxymethylene homopolymer which has a coefficient of friction of about 0.3. 
   Other lubricants and lubricant systems for acetal copolymers may be used. For example, a polyolefin or a blend of polyolefin and PTFE have been found useful as a lubricant or lubricant system in acetal copolymers. Suitable polyolefins include polyethylene, polypropylene and polyolefin copolymers, such as ethylene-propylene copolymer, etc. Since polyolefins are less expensive than PTFE, it may be desirable to replace as much of PTFE as possible with polyolefin. As reported in Example 3 of U.S. Pat. No. 5,216,079, the addition of 20% low density polyethylene (USI Microthene MN-703-6) to CELCON M90 results in a decrease in coefficient of friction and improved wear resistance as compared to oxymethylene copolymer lubricated with 20% PTFE (LNP TL-140). Other lubricants such as molybdenum disulfide, graphite power, silicone fluid, etc. may also be part of the lubricant system and replace some or all of the PTFE. For example, LUBRILOY KL (product code 741-170-200) sold by LNP Engineering Plastics, Inc. has a CELCON M270 matrix with a lubricant system that eliminates the PTFE but which has a wear resistance and coefficient of friction (0.03 static, LNP#3) that is better than CELCON M270 lubricated with PTFE. In addition, the materials used in the LNP&#39;s lubricant system are less expensive than PTFE. 
   LUBRILOY KL acetal copolymer is provided as pellets from which slide  10  can be injection molded using conventional ram or reciprocating screw injection molding machines. If a mirror finish is desired, the mold can be polished to a very smooth finish and then chrome plated. In addition to enhancing the physical appearance of slide  10 , the mirror finish also lowers the coefficient of friction. 
   As shown in  FIG. 1 , non-slip resilient pad  20  is seated in recess  18  and adhered to upper face  12 . A tear resistant fabric  32  may be applied to pad  20 . Pad  20  projects above rim  22  and is formed of a compressible material. Pad  20  may project from about 0.05 to 0.25 inches above rim  22 , preferably from 0.05 to 0.15 inches and most preferably about 0.07 inches. Compressible material is preferably softer than latex rubber or ethylvinylacetate (EVA) which are used on slides made under the &#39;699 patent and may be a cellular urethane foam. A material sold as HyPUR-cel-T-0812 by Rubberlite Inc. with a density 104–152 g/cm 3  has been found satisfactory for pad  20 . The leg or base of the object being moved settles into pad  20  which is softer than EVA so that the object does not tend to come off the slide. In the event that the object does shift, the leg or base tends to be stopped by rim  22 . 
   In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.