GB1575034A

GB1575034A - Method of manufacturing a helically grooved plastics bearing

Info

Publication number: GB1575034A
Application number: GB3834/77A
Authority: GB
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1976-02-03
Filing date: 1977-01-31
Publication date: 1980-09-17
Also published as: NL7601060A; DE2702302A1; IT1077604B; BE850984A; FR2340183A1; SE7700993L; JPS5294952A

Description

(54) METHOD OF MANUFACTURING A HELICALLY GROOVED PLASTICS BEARING (71) We, N.V. PHILIPS' GLOEILAMPENFABRIEKEN, a limited liability Company, organised and established under the laws of the Kingdom of the Netherlands, of Emmasingel 29, Eindhoven, the Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method of manufacturing a plastics rotationally symmetrical bearing of which a rotationally symmetrical surface is provided with a helical lubricantpumping groove or a pattern of such grooves.

A great difficulty in manufacturing bearings of the above kind is the provision of the helical groove or grooves in the rotationally symmetrical surface of the bearing.

A possible method consists in coating a smooth mould element with synthetic resin, removing the resulting sleeve from the mould element and cutting the desired grooves in the bearing surface by a machining process. This method is very time-consuming and cannot be used to make bearings with small inside diameters.

Another possible method consists in screwing the moulded product off the mould element.

For bearings having a pattern of grooves of a single hand this may be done with a screwing in one direction but it is comparatively time-consuming.

For a cylindrical bearing which is open at both ends and has patterns of grooves of opposite hands which pump in opposition to each other, two mould pins situated in line and each having a pattern of helical grooves may be coated with synthetic resin and subsequently screwed in opposite directions out of the plastics sleeve thus formed. In addition to the fact that this method is time-consuming, it is very difficult to arrange the mould pins exactly in line with each other in the axial direction.

It is an object of the invention to provide a method by which small plastics bearings can be readily mass-produced.

In the method according to the invention a mould element having a helical ridge or a pattern of helical ridges of which the height. width and pitch correspond to the depth, width and pitch of the groove or grooves to be formed is covered with a synthetic resin and subsequently the article formed by the resin is pulled from the mould element in the axial direction without relative rotation between the article and the mould element. It has surprisingly been found that in this method substantially no damage to the helical groove or grooves occurs when the bearing is pulled off the mould pin. The synthetic resin permits sufficient elastic deformation of the bearing as it is drawn off the pin to avoid such damage. The manufacturing time is very short and different patterns of grooves can be provided in the relevant surface. if desired.

Preferably. the dimensions of the bearing are selected so that$ < 0.3 ;* > 0.1 and 0.2 < < 2. and the bearing material is selected so that at least one of the two following conditions is satisfied: P 2 2.2L a2h (-) > ( - 1) E R L2R P 2 20t/R - 2 a2h + 0.2) E 7.1R/L + 1.5 L2R wherein P = maximum permissible surface pressure of the bearing material, E = elasticity modulus of the bearing material, t = the thickness of the bearing wall at the bottoms of the grooves, R = the radius of the bearing surface between the grooves, h = depth of the grooves, a = width of the lands between the grooves, L = length of the bearing When the above conditions are satisfied, a bearing is obtained which can readily be removed axially from the mould element without damage occuring which might interfere with the satisfactory operation of the bearing. In this manner a method is obtained with which it is possible to manufacture bearings of the kind described in a comparatively rapid, cheap and simple manner.

An example of the method according to the invention will now be described in greater detail with reference to the accompanying drawings, in which Figure 1 is a side view, partly in cross-section and not drawn to scale, of a mould element in the form of a pin provided with two patterns of helical ridges, the pin being shown surrounded by a mould, Figure 2 is a cross-sectional view, not drawn to scale, of a cylindrical bearing, bush made with the mould pin and mould shown in Figure 1, and Figures 3 to 5 show other embodiments of bearings which can be made by the method according to the invention.

Reference numeral tin Figure 1 denotes a cylindrical pin which has two patterns 2 and 3 of helical ridges. The -helical ridges of the two patterns are of opposite lands. Around the pin there is arranged a divided hollow cylindrical mould 4 which has an aperture 5 through which a synethetic resin in liquid form can be injected into the cavity 6 between the mould 4'and the pin 1. After the cavity 6 has been filled and the synthetic resin hardened, the mould 4 is removed and the plastics article formed around the pin 1 is pulled off in the axial direction of the pin 1 without relative rotation between the article and the pin. The resulting bearing is shown in the cross-sectional view of Figure 2.

It has surprisingly been found that pulling the bearing axially from the mould pin causes substantially no damage to the helical grooves produced by the ridges 2 and 3 of the mould pin.

In particular. this method has proved to result in a good bearing when the following conditions are satisfied: h - < 0.3 a - 0.1 and R R 0.2 < - < 2.

L and furthermore when the bearing material is selected so that at least one of the following conditions is satisfied: P 2 2.2L a2h (-) > ( -1)- E R L2R P 2 20t/R - 2 a2h (-) > ( +0.2)- E 7.1 R/L + 1.5 L2R wherein t = thickness of the bearing wall at the bottoms of the grooves, R = the radius of the bearing surface between the grooves, h = depth of the grooves, a = width of the lands between the grooves, L = length of the bearing, P = maximum permissible surface pressure of the bearing material E = elasticity modulus of the bearing material.

In a practical case the dimensions of the bearing were chosen as follows: t = 0.8 mm R = 1.25 mm h = 0.01 mm a = 0.15 mm L = 4.5 mm while for the bearing material a synthetic resin was chosen in which P = 50 kgf/cm2 E = 9000 kgf/cm2.

Such a bearing is very suitable for being manufactured by the above-described method.

Although the example of Figure 2 shows a bearing bush having two patterns of helical grooves in its inner surface, it is alternatively possible to manufacture in this manner a bearing bush having patterns of grooves in its outer surface.

Furthermore. the method according to the invention can also be used for manufacturing bearings other than the cylindrical bearing shown in Figure 2. which is open at both ends; for example. it can be used to manufacture the cylindrical bearing shown in Figure 3. the conical bearing shown in Figure 4 and the spherical bearing shown in Figure 5. all of which are open at only one end. Naturally in these cases the mould would be adapted to the shape of the bearing.

WHAT WE CLAIM IS: 1. A method of manufacturing a plastics rotationally symmetrical bearing of which a rotationally symmetrical surface has a helical lubricant-pumping groove or a pattern of such grooves. wherein a mould element having a helical ridge or a pattern of helical ridges of which the height. width and pitch correspond to the depth. width and pitch respectively of the groove or grooves to be formed is covered with a synthetic resin and subsequently the article formed by the resin is pulled from the mould element in the axial direction without relative rotation between the article and the mould element.

2. A method as claimed in Claim 1 wherein the dimensions of the bearing are selected so thatha < 0.2* > 0.1 and 0.2 < < + < 2. and the bearing material is selected so that at least one of the following conditions is satisfied: p 2 2.2 L a2h (-) > (- 1) E R L2R p 2 20 t/R - 2 a2h (-) > (---------- + 0.2)- E 7.1 R/L + 1.5 L2R wherein P = maximum permissible surface pressure of the bearing material.

E = elasticity modulus of the bearing material.

t = thickness of the bearing wall at the bottoms of the grooves.

R = radius of the bearing surface between the grooves.

h = depth of the grooves.

a = width of the lands between the grooves.

L = length of the bearing.

3. A method of manufacturing a helically grooved bearing as claimed in Claim 1.

substantially as herein described with reference to Figure 1 and Figure 2. 3. 4 or 5.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. P 2 2.2L a2h (-) > ( -1)- E R L2R P 2 20t/R - 2 a2h (-) > ( +0.2)- E 7.1 R/L + 1.5 L2R wherein t = thickness of the bearing wall at the bottoms of the grooves, R = the radius of the bearing surface between the grooves, h = depth of the grooves, a = width of the lands between the grooves, L = length of the bearing, P = maximum permissible surface pressure of the bearing material E = elasticity modulus of the bearing material. In a practical case the dimensions of the bearing were chosen as follows: t = 0.8 mm R = 1.25 mm h = 0.01 mm a = 0.15 mm L = 4.5 mm while for the bearing material a synthetic resin was chosen in which P = 50 kgf/cm2 E = 9000 kgf/cm2. Such a bearing is very suitable for being manufactured by the above-described method. Although the example of Figure 2 shows a bearing bush having two patterns of helical grooves in its inner surface, it is alternatively possible to manufacture in this manner a bearing bush having patterns of grooves in its outer surface. Furthermore. the method according to the invention can also be used for manufacturing bearings other than the cylindrical bearing shown in Figure 2. which is open at both ends; for example. it can be used to manufacture the cylindrical bearing shown in Figure 3. the conical bearing shown in Figure 4 and the spherical bearing shown in Figure 5. all of which are open at only one end. Naturally in these cases the mould would be adapted to the shape of the bearing. WHAT WE CLAIM IS:

1. A method of manufacturing a plastics rotationally symmetrical bearing of which a rotationally symmetrical surface has a helical lubricant-pumping groove or a pattern of such grooves. wherein a mould element having a helical ridge or a pattern of helical ridges of which the height. width and pitch correspond to the depth. width and pitch respectively of the groove or grooves to be formed is covered with a synthetic resin and subsequently the article formed by the resin is pulled from the mould element in the axial direction without relative rotation between the article and the mould element.