1. Field of the Invention
The invention relates to pre-reduction equipment for guiding a pipe blank and reducing its end before it enters an "Assel" rolling mill, which is disposed immediately downstream from the pre-reduction equipment. The mill consists of several freely rotatable rollers, which are disposed uniformly distributed about the pipe blank and can be set concentrically against the pipe blank and the setting motion of which can be controlled as a function of a determined position of the pipe blank.
2. Description of the Related Art
Pre-reduction equipment of the generic type are known, for example, from the DE 38 23 135 C 2. They are used in order to avoid funnel-shaped triangular end parts of pipes rolled from pipe blanks in "Assel" rolling mills. Such triangular end parts arise in the process due to the fact that the end of the pipe, when rolled, expands. In the DE 38 23 135 C 2, in order to avoid these trumpet-shaped pipe ends, it is proposed that the diameter of the end part of the pipe blank be pre-reduced, before it runs into the reduction zone of the "Assel" rolling mill. As pre-reduction equipment, freely rotatable rollers are used, which, when viewed in the rolling direction, are disposed in a stand in front of the "Assel" rolling mill. The four rollers, distributed over the periphery of the pipe blank, can be adjusted concentrically with respect to the pipe blank. Shortly before the end part of the pipe blank enters this pre-reduction equipment, the rollers are switched on and the end part of the pipe blank is reduced in this way. In principle, this pre-reduction equipment has proven its value.
For the initial rolling of the pipe blanks in the "Assel" rolling mill it is necessary to push these blanks so far between the "Assel" rollers so that the latter take hold of the pipe blank. In this connection, it is known that the pipe blank can be clamped at its end so that it cannot rotate and be pushed with the front end into the rolling gap. It is a disadvantage that the pipe blank, so clamped, is twisted in the clamping device, if it is not released in good time. It is furthermore known that a contact shoulder can be provided at the mandrel rod, over which the pipe blank is pushed into the rolling gap. This has the disadvantage that the shoulder can be adjusted as a function of the length and must be geared to the dimensions of the pipe blank, which is to be subjected to an initial rolling process, that is, it must be exchangeable.
A special problem of the initial rolling of the pipe blanks arises when particularly short pipe blanks are used, because the feeding apparatuses have an inadequate lift for pushing the start of the pipe blank securely into the rollers of the "Assel" rolling mill. This is a problem particularly when the pipe blanks must be pushed in by means of the known pre-reduction equipment which, due to the method, must occupy a position at a certain distance from the "Assel" rolling mill.