The invention relates to the field of what is internationally known as horizontal directional drilling (HDD). HDD is a technique which is much applied for laying pipelines under rivers, canals and roads for the purpose of underground infrastructure, such as water pipes, telecommunication cables and electricity cables.

An HDD machine (internationally known as HDD rig) is equipped for this purpose with a mast with racks for guiding a drill drive for a drill pipe. In the relevant field such a mast is known with racks welded thereto. Applicant markets an alternative mast, which is provided with a manhole for mounting the racks on the mast with bolts.

The present invention relates to an assembly for forming a mast for guiding a drill drive in an HDD machine, which assembly comprises:a mast body with a generally U-shaped cross-section;a mast cover with a recessed surface;a set of two or more racks;first connecting means for connecting the racks releasably to the mast cover;and second connecting means for connecting the racks releasably to the mast body, wherein the racks together with the mast body and the mast cover in assembled state form a mast with a closed contour.

The present invention also relates to a method for forming the mast from an assembly according to the invention, which method comprises the following steps of:

a) mounting the racks on the mast cover;

b) placing the mast cover and the racks on the mast body; and

c) mounting the racks on the mast body.

The assembly and the method according to the invention make it possible to assemble the mast from carefully selected components and materials and at any desired location. The racks, which are wear parts, can in particular be replaced faster and under better working conditions. This is because it is no longer necessary to mount them from the inside, and the manhole can be dispensed with. As a result, the mast can also take a more compact form.

In a first preferred embodiment the mast body is provided with support surfaces for the racks. The support surfaces simplify the mounting of the mast considerably.

According to a further development of the first preferred embodiment, the mast body is provided with bent edges which form the support surfaces. These bent edges form integrated support surfaces which enable integral production in advantageous manner.

In an optimal development of the first preferred embodiment the assembly further comprises a set of two or more strengthening strips for placing against the support surfaces. The strengthening strips support the racks and increase the loadability of the mast. The strengthening strips moreover enable a choice of different materials for the racks and the mast body.

In a practical preferred embodiment the first and/or the second connecting means are bolts.

According to a first preferred embodiment, the method according to the invention further comprises the step of selecting an assembly with strengthening strips, wherein step c) comprises the following sub-steps of:

c1) placing the strengthening strips against the support edges;

c2) connecting the racks to the support edges and the strengthening strips.

According to an optimal development of the first preferred embodiment of the method, step a) further comprises of placing a plurality of racks adjacently on one or both longitudinal sides of the mast cover and step c) comprises of connecting the strengthening strips to the support edges such that in assembled state of the mast one or more of the strengthening strips overlap the adjacent racks. The racks and the strengthening strips thereby come to lie in brick bond pattern, which will result in a better load distribution during use of the mast.

The invention also relates to a mast formed from the assembly according to the invention or by the method according to the invention.

