Shot blast machine with hold down for parts being deflashed

A shot blast machine for deflashing plastic molded parts in which a substantially horizontal conveyor belt is used for delivering the parts to be deflashed. Shot blasting wheels are located above the conveyor belt and impel particles downward into deflashing engagement with plastic parts on the conveyor. A wire mesh member, in the form of an endless belt, is positioned above and in close proximity to the conveyor belt so that parts being blasted are trapped and held between the wire mesh belt and the conveyor belt. The wire mesh belt prevents the parts being deflashed from being moved off the conveyor belt under the influence of blasting particles. The hold down belt is also movably mounted above the conveyor belt so that it can float up and down and accommodate parts of different sizes.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates generally to the field of shot blasting and more 
particularly to a shot blast machine for deflashing thermoset molded 
plastic parts. 
Many industrial parts that are made of plastic can be molded and 
substantially deflashed with abrasive particles that are projected at the 
parts. A system that uses abrasive particles thus lends itself to 
continuous operation and is advantageous because of its efficiency. This 
further eliminates manual deflashing and provides for an increased 
production relative to typical batch systems. The result is a higher 
capacity than other deflashing systems. 
The machine of this invention provides a hold down assembly which 
cooperates with a continuous endless conveyor belt. The hold down is 
required for light and small parts, since the kinetic energy created by 
the blast stream of particles will move the parts on the belt and thereby 
fail to provide the correct exposure time of the parts to the particle 
stream for deflashing. The hold down assembly includes a wire mesh member 
which keeps the plastic molded parts on the conveyor while abrasive 
particles are propelled through the wire mesh to deflash the parts. In 
this manner, the present system eliminates the moving of parts and 
provides high production in a controlled process to thereby achieve a 
continuous finishing of the plastic molded parts. Furthermore, the system 
is ideally suited for handling larger parts that cannot be tumbled and 
smaller, fragile parts that are prone to breakage or nicking. 
The machine of the present invention thus includes a continuous, variable 
speed conveyor system in conjunction with a hold down assembly to provide 
non-stop deflashing via a centrifugal blasting system with variable speed 
centrifugal blast wheels that thoroughly blast the parts. An adjustable 
blow off system can also be employed to remove light or medium amounts of 
carryout abrasive particles. A polyamid/polycarbonate blasting media is 
preferred as the abrasive particles since it causes virtually no surface 
alterations on the plastic parts while still providing sufficient mass for 
the deflashing process. This simple yet rugged construction of machine 
assures minimal and easy maintenance and repairs. 
Further features and advantages of the blast machine of this invention are 
as follows: 
A. The wire mesh member, in the form of an endless belt, is provided 
generally parallel to the conveyor belt and functions to hold down or 
press light weight parts on the conveyor belt so that the parts will not 
slide off the conveyor belt. 
B. The wire mesh belt and the conveyor belt are synchronized in their 
speeds of travel so that speed differences will not result in the creation 
of scratch marks on the plastic parts. Scratch marks can result if the 
parts roll or slide relative to either of the belts. 
C. The drive system for the hold down belt is connected to the drive system 
of the conveyor belt via gearboxes or chains. This assures synchronized 
movement of the belts. 
D. The wire mesh belt is made of a low density mesh so that the blast 
wheels can project the blast media through the wire mesh and into 
engagement with the parts to be deflashed on the conveyor below. 
E. The mesh or hold down belt is "floating". Stated otherwise, it is 
mounted in the machine so it can move up and down relative to the conveyor 
belt to thereby accommodate parts of different thicknesses. 
Further objects, features and advantages of the invention will become 
apparent to those skilled in the art from a consideration of the following 
description and the appended claims, when taken in connection with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to the drawing, the blast machine of this invention is 
indicated generally at 10 in FIG. 1. The blast machine 10 is comprised of 
a main frame 12, a blast wheel 14, a conveyor belt assembly 18 and a hold 
down assembly 20. The blast wheel 14 is of conventional construction and 
impels abrasive plastic particles in stream 16 toward the generally 
horizontal conveyor belt assembly 18 while the hold down assembly 20, 
which includes an endless, wire mesh belt 24 positioned in the machine 10 
above the conveyor belt 18 and below the blast wheel 14, holds down or 
retains plastic parts 22 to be deflashed on an endless belt 25 of the 
conveyor assembly 18. 
As particularly shown in FIGS. 5 and 6, the hold down assembly 20 includes 
an endless wire mesh belt 24 which is rotatably mounted on a drive pulley 
26 at one end and a larger pulley 28 at the opposite end, both of which 
are supported by a frame 44. The drive pulley 26 is driven by a gear box 
50 located on the shaft 30 for the pulley 26. The gear box 50 is connected 
via a shaft 52 to the gear box 54 for the conveyor 18. As indicated in 
FIG. 5, the wire mesh belt 24 is shown as having mesh density that 
provides a multitude of large openings 42 for the particles in the stream 
16 to pass therethrough and impact the parts 22 located below. 
The conveyor assembly 18 includes an endless belt 25 on which the parts 22 
to be deflashed are supported during movement through the machine 10. The 
conveyor belt 25 is positioned about a pair of end pulleys 27 and 29 and 
driven by a motor 31 whose output shaft 33 causes movement of a belt 35 
connected with the pulley 27 (FIG. 1). In use, the top section of the belt 
18 moves to the right as viewed in FIG. 4b and indicated by the arrow 40. 
Additionally, the endless conveyor belt 25 extends longitudinally beyond 
both ends of the hold down assembly 18 as generally defined by the pulleys 
27 and 29. Those portions of the conveyor belt 25 which extend beyond the 
ends of the wire mesh belt 24 are respectively referred to and used as an 
inlet section 36 and a discharge section 38 of the conveyor assembly 18. 
As illustrated in FIG. 2, the connector shaft 50 extends between the gear 
box 52 of the hold down assembly 20 and the gear box 54 for the conveyor 
assembly 18. This connection of the two assemblies 18 and 20 synchronizes 
the wire mesh belt 20 so that it moves at the same speed of travel as the 
conveyor belt 25. Obviously, other mechanical and non-mechanical 
mechanisms can be used for synchronization of the belts 24 and 25, 
including a controller synchronizing separate drive motors (not shown). 
Referring now to FIGS. 4a-4c, parts to be deflashed are deposited on the 
inlet section 36 of the conveyor belt 18. The frame 44 of the hold down 
assembly 20 is pivotably supported at horizontal pivot members 46 by a 
pair of arms 48 that are in turn pivotally mounted at 49 to the main frame 
12 at a point downstream from the belt inlet section 36. The mounting of 
the frame 44 and assembly 20 to the ends of the arms 48 generally at a 
midway point on the frame 44 between the pulleys 26 and 28 and enables the 
hold down assembly 20 to "float" or move up and down relative to the 
conveyor assembly 18. This floating allows for the accommodation of 
various sized parts 22 as they pass between the upper flight of the 
conveyor belt 25 and the lower flight of the wire mesh belt 24. 
As shown in FIG. 4a, the parts 22 to be blasted and deflashed are advanced 
by conveyor belt 25 to a position where they initially engage the wire 
mesh belt 24. Movement of the conveyor belt 25 in the direction of arrow 
40 acts on the parts 22 to move the parts 22 under the lead pulley 28 of 
the assembly 20. This initial engagement of the parts 22 with the lower 
flight of the wire mesh belt 24 causes this end of the assembly 20 to 
pivot upwardly, as indicated by the arrow 60 in FIG. 4b. As the parts 22 
continue to move from left to right, while being held down by the wire 
mesh belt 24, the middle section (generally at pivot 46) of the assembly 
20 and its trailing end (generally at the drive wheel 26) move upward, as 
indicated by arrow 61, relative to the conveyor belt 25 and in response to 
the presence of the parts 22. 
While between the belts 24 and 18, the parts 22 are readily subjected to 
the blasting action of the abrasive plastic particles in the stream 16 
from the blast wheel 14. This blasting and deflashing continues as the 
parts 22 advance toward the discharge section 38 of the conveyor belt 25. 
This process is continuous as a media conveying element (not shown) 
operates to convey the blast particles from positions below the conveyor 
belt 25 to the blast wheel 14 for discharge into the stream 16. In this 
manner, the process performed by the present invention can continuously 
deflash parts 22 over a prolonged period of operation. 
It is thus been seen that in the blast machine 10 of this invention, the 
parts 22 to be deflashed are held on the conveyor belt 18 by the wire mesh 
belt assembly 24 to assure complete deflashing of the parts 22 as they 
move beneath the blast wheel 14 and toward the discharge end 38 of the 
conveyor belt 18. The resulting continuous process is efficient and 
reliable at deflashing since all of the parts are held beneath the blast 
wheel 14 and cannot be moved off of the conveyor belt 18 as a result of 
impact with the abrasive particles in the stream 16. 
A parts separator 70 (FIG. 4a) eliminates the layering of parts 22 on the 
parts conveyor 18. This eliminates the resulting mashing of parts by each 
other. The separator 70 includes brushes 72 which push the upper layers of 
parts backward until the space on the conveyor 18 allows a proper deposit. 
It is to be understood that the invention is not limited to the exact 
construction illustrated and described above, but that various changes and 
modifications may be made without departing from the spirit and scope of 
the invention as defined in the following claims.