METHOD FOR TREATING ARTICLES WITH PLASTIC

Abstract: A method for applying a coating of plastic on a metal shaft, wherein: (i) plastic is applied onto the shaft by means of injection moulding; (ii) an extruded plastic sleeve cut to the right length is placed on the shaft; (iii) the plastic is sprayed onto the shaft with the aid of a sprayer; (iv) the plastic is applied by lowering the shaft into a plastic solution; (v) plastic is applied in powder form onto the heated metal of the shaft; characterised in that after the plastic has been applied, a metal sleeve is moved relative to a shaft and the plastic applied thereto at the same time as the whole unit is supplied with ultrasound to calibrate the plastic sleeve on the shaft.

Description: METHOD FOR TREATING ARTICLES WITH PLASTIC Method for coating shafts with plastic. The present invention relates to a method for coating an article with plastic. The invention is especially directed towards the coating of shafts with plastic, and the new method makes use of an ultrasound source. The method entails a favourable production solution for depositing a toleranced sliding surface of plastic on metal shafts in a more accurate way than with today's solutions. The metal shafts are preferably made of steel, aluminium or manganese, but the invention is not limited to coating these metals. The products that are coated by means of the inventive method may, e.g., be sliding surfaces on shafts that are used as steering wheel columns in cars. Great precision is required here to be able to move the steering wheel back and forth and to absorb impact in the event of a collision. Today, there are several known methods of coating a shaft. One previously known method is to use injection moulding, where a shaft is placed inside a mould, and plastic is injected into the mould at high pressure. A second method is to use an extruded plastic sleeve which has been cut to a suitable length and is of the right shape and size. The plastic sleeve is passed onto the shaft, heat is subsequently applied to shrink the plastic and then ultrasound to calibrate the plastic on the shaft against the sleeve. By calibrating the shaft against the sleeve the proportions are adjusted so they are within the tolerances when the shaft is passed into the sleeve at the same time as ultrasound is applied. This is done to obtain better adaptation of the plastic coating and the sleeve than earlier, as the sleeves have different shapes and sizes. Another method is to use a plastic powder which is applied to a heated metal. The temperature in the process must be higher than the melting point of the plastic. In this way the powder will form a thin layer of plastic on the metal. The present invention is based on known technology and exploits it further to make products having a greater accuracy within specified tolerance limits. With the inventive method it is possible to operate easily within tolerance limits of from +/-3/100 to +/- 3/1000. According to the invention, the point of departure is one of the above-outlined methods of depositing plastic on a shaft, and then moving a metal sleeve over the shaft and plastic sleeve, whilst ultrasound is employed to calibrate the plastic on the shaft. The present invention is directed towards a method for applying a coating of plastic on a metal shaft, wherein: (i) plastic is applied onto the shaft by means of injection moulding; (ii) an extruded plastic sleeve cut to the right length is placed on the shaft; (iii) the plastic is sprayed onto the shaft with the aid of a sprayer; (iv) the plastic is applied by lowering the shaft into a plastic solution; (v) plastic is applied in powder form to the heated metal of the shaft; characterised in that after the plastic has been applied, a metal sleeve is moved relative to a shaft and the plastic applied thereto at the same time as the whole unit is supplied with ultrasound to calibrate the plastic sleeve on the shaft. The invention will be explained in more detail below with reference to: Figure 1 which is a schematic illustration of a shaft and a metal sleeve. The figure shows a device 10 on which a shaft 11 is mounted, which, e.g., may be made of steel, aluminium or manganese. A plastic sleeve 12 has been applied to the shaft. The device 10 also consists of a metal sleeve 13 which is complementary to the shaft 11. The whole unit is placed in an ultrasound apparatus (not shown). The ultrasound apparatus will have special properties as regards ultrasonic strength, dimension and shape, but is not limited to a specific model. The device 10 also has a means which can move the shaft 11 back and forth and in and out of the metal sleeve 13. Alternatively, the metal sleeve 13 can be moved back and forth over the shaft 11 , which remains stationary. The ultrasonic waves will initiate vibrations in the plastic and the shaft, and ensure that the surface of the plastic sleeve 12, on account of the frictional heat, melts/shrinks and takes the shape of the external sleeve 13. On the figure the ultrasonic waves are indicated by means of the arrows 15 directed towards the metal sleeve 13. Alternatively, an extruded plastic sleeve can be used. Again the extruded plastic sleeve is placed on a shaft 11 in the same manner as outlined above in an apparatus where ultrasonic waves generate frictional heat so that the plastic melts and shrinks against the shaft. As regards the types of plastic used in the process, it is possible to use different types, provided that they have the desired properties. The time it takes to produce a plastic-coated shaft may be from 20 to 60 seconds depending upon the production line. The plastic can be deposited on the shaft 11 at a temperature of from about 200-300°C, whilst the temperature during calibration is between 20° and 60°C. The temperature during calibration is important with a view to tolerances, and this must be taken into account in the event of, e.g., increased cycle time or extra cooling prior to calibration. By using the inventive method, articles of high accuracy and precision can be produced within specified tolerance limits. The products made following the inventive method attain a much greater precision than the solutions known at present.

Claims: P a t e n t c l a i m s 1. A method for applying a coating of plastic on a metal shaft (11), wherein: (i) plastic is applied onto the shaft by means of injection moulding; (ii) an extruded plastic sleeve cut to the right length is placed on the shaft; (iii) the plastic is sprayed onto the shaft with the aid of a sprayer; (iv) the plastic is applied by lowering the shaft into a plastic solution; (v) plastic is applied in powder form to the heated metal of the shaft; characterised in that after the plastic has been applied, a metal sleeve (13) is moved relative to a shaft (11) and the plastic (12) applied thereto at the same time as the whole unit is supplied with ultrasound to calibrate the plastic sleeve on the shaft. 2. A method according to claim 1, characterised in that the metal sleeve (13) moves whilst the shaft (11) remains stationary. 3. A method according to claim 1 , characterised in that the shaft (11) with plastic applied thereto moves whilst the metal sleeve (13) remains stationary. 4. A method according to claim 1, characterised in that the plastic (12) is applied to the shaft (11) at a temperature of from about 200-300°C. 5. A method according to claim 1 , characterised in that the shaft (11) and plastic are cooled to about 20°-60°C prior to calibration. 6. A method according to claim 1 , characterised in that plastic is coated onto a metal sleeve which is then calibrated against the shaft (11).

Inventors: STENERUD LARS S, STENERUD, LARS, S.
Applicants: PLASTO AS, STENERUD LARS S, STENERUD, LARS, S.
Application year: 1998
Main classification: B29C70
IPC codes: B29C63, B29C70